1. Field of the Invention
The present invention generally relates to recording/reproducing devices, and particularly relates to a recording/reproducing device which replaces a defective sector on a recording media.
In recent years, there has been a demand for lowering the costs and increasing the volume of recording/reproducing devices. In the recording/reproducing devices, a test for a recording media is conducted to ensure reliability of the devices. If defective sectors are found on the recording media during the test, these sectors are replaced by other sectors. Since the number of defective sectors increases with an increase in the total number of sectors, it takes a longer time for testing devices having a larger volume. Thus, there is a need for a method of shortening the test time without compromising the reliability of the devices.
2. Description of the Prior Art
In the magnetic disk drive of the prior art, an analog examination was the main type of tests for the recording media, in which read signal patterns from the media are inspected to detect portions of excessively large magnitudes or excessively small magnitudes. These portions are then identified as defective sectors. However, lower costs and mass-scale manufacturing of the devices has resulted in digital tests being the majority of the media tests. Digital tests are conducted by writing data and detecting errors to identify the defective sectors.
Regardless of the type of tests, i.e., digital tests or analog tests, the number of defective sectors increases with an increase in the total number of sectors, which leads to a longer test time and increased manufacturing costs.
Tests which require less time include tests based on automatic replacement processing and verification processing. The automatic replacement processing searches for the defective sectors during the formatting of a disk, and these defective sectors are replaced by spare sectors automatically. The verification processing checks if a given sector is defective by reading data from the sector immediately after the data is written in the sector.
There is another method in which ECC (error correction code) and offset-read are used for recovering data for a disk in combination with the use of the automatic replacement processing. In this method, if defective sectors are generated and data cannot be recovered, then, these sectors are replaced to enhance the reliability.
FIG. 1 shows an illustrative drawing for explaining the replacement of the sectors. FIG. 1 shows sectors 0 to 12 arranged on one track. If LBA (logical block address) 6 is detected as a defect, for example, one of the spare sectors replaces the defective sector and becomes a new sector 6.
FIG. 2 shows a testing method of the prior art. FIG. 2 is concerned with the treatment of small defects in magnetic disk devices. At a step S101, defective sectors are detected during the formatting of a disk, and unrecoverable defective sectors are automatically replaced. At a step S102, long-hour running which lasts for several hours per one surface of the disk is conducted. During the long-hour running, a functionality test and a reliability check are conducted by using an ECC function and a format/certify function, and, also, small defects are detected and replaced. At a step S103, the device is shipped out from a factory. This test tries to minimize the number of small defects.
As described earlier, the automatic replacement function automatically replaces sectors generating read errors with spare sectors. However, read errors can be generated by causes other than media damages so that some sectors with read errors do not have to be necessarily replaced. Examples of such read errors are errors which occur in a large number with small repeatability under bad conditions, including errors occurring due to external noise (electromagnetic fields), vibrations, mechanical off-track, peculiarity of head materials, electromagnetic conversion characteristics, etc.
Even if a given sector has errors of high repeatability, the sector might not have media damage. For example, such errors include an error caused by off-track writing which results from an impact applied during the writing of data. Another example of such errors is an error caused by debris of data which is left when the writing of data is terminated because of power-cut and the like.
When sectors having no media defect are replaced by spare sectors, the number of used spare sectors increases so as to fill the spare sector area. This leads to a shorter life and a lower performance of the devices. Also, when the number of rewrites is limited in a given media, blocks whose rewrite numbers have already exceeded a limit might be used for replacing blocks after the formatting of a disk. This leads to lower reliability of the device.
There are several methods proposed for countering these problems. Such methods are, for example, disclosed in Japanese Laid-Open Patent No. 5-135502 and No. 4-106764. Japanese Laid-Open Patent No. 5-135502 teaches providing two pointers indicating replacing blocks for a media with a limited number of rewrites. When replacement is provided by using the first pointer, the process of the replacement is completed. In doing so, the reliability of the media is enhanced by avoiding the use of blocks exceeding a rewrite limit.
Japanese Laid-Open Patent No. 4-106764 teaches replacing defective bytes and several other bytes in the proximity thereof. That is, an effective use of the spare area is realized by replacing only a defective portion of a sector and a few adjacent bytes instead of the whole sector.
Also, other methods have been proposed to counter a problem that errors occur first time at the time of writing data in an unused space which has not been accessed by the host device. Other methods have been proposed to enhance detectability of defects.
However, the techniques disclosed in these two patent applications described above have a problem in that user data is lost when the replacement process is terminated by a power-cut, a reset or other reasons.
In a small magnetic drive using a magnetic disk smaller than 3.5 inches, an MPU (micro processor) of the drive tends to have a limited performance. Thus, when the automatic replacement function is incorporated in such a device, this limited performance leads to a longer processing time. Also, when a host device connected to the magnetic drive has a limited performance, time out may be detected during the replacement process.
Also, when the environment for using the device is not stable and the device is easily influenced by noise, vibration, temperature changes, etc., a replacement process solely dependent on the detection of read errors may lead to the use of all the spare sectors. Thus, the life of the device is shortened, and the reliability is compromised.
Accordingly, there is a need in the field of recording/reproducing devices for a recording/reproducing device and a method of replacing defective sectors which can shorten the time required for replacing defects and can enhance the reliability.